This invention relates to stamping designs from a continuous metal leaf onto a continuous moving substrate web with minimum waste of leaf, more particularly, to in-line hot stamping of metal leaf in an in-line gravure ink printing machine.
Methods for stamping a metal leaf on packaging material are well known. A hot rotary stamper utilizes a die mounted on a rotating roller to accomplish the transfer of material onto a substrate using pressure, elevated temperature, and time. Hot rotary stamping is particularly well suited for continuous stamping processes.
Metal leafs may be stamped onto substrate webs used in the packaging industry. The application of metal leaf is desired because it is more reflective than inks and is preferred for marketing and aesthetic reasons.
Hot stamping of packaging material has been traditionally carried out in a two step process. The first step is printing of the substrate material with the desired decorative design on an in-line printing machine during continuous advance of the substrate. The second step is to perform the hot stamping of metal leaf on discrete sheets of substrate while held stationary in a hot stamping press. Thereafter, the stamped sheets may be subjected to a third step whereby the stamped portions may be printed with inks.
One of the problems with the known hot stamping techniques is to make efficient use of the metal leaf which is a relatively expensive component of the packaging materials. Sheet stamping provides for efficient use by minimizing the amount of waste, but involves an additional expense of a separate stamping station and the time required to perform the stamping operation.
Techniques for continuously advancing the leaf at the same speed as the substrate for in-line stamping are known but they involve an unacceptable waste of leaf between stamping locations. Such techniques include making a stamp by superpositioning a metal leaf and a substrate web, moving at the same velocity, between a die roller having one or more raised dies and a back-up roller rotating at the same velocity as the metal leaf and the substrate web. The stamp is made at the point where a raised die forces the metal leaf and the substrate web against the backup roller with sufficient force to transfer the metal leaf to the substrate web. These techniques provide that this point is where a raised die is aligned with the centers of the die roller and the back-up roller.
It is therefore, an object of this invention to provide an improved apparatus and method for advancing thin metal leaf at a variable velocity for stamping metal leaf on a moving substrate and con serving metal leaf.
It is another object to use the stamping mechanism itself to accelerate the leaf to the speed of the substrate necessary for stamping.
It is a further object of this invention to provide a means for accelerating and decelerating the metal leaf which is electronically controlled.
It is a further object of this invention to provide for unevenly spacing the stamps in a repeating pattern on the substrate web.
It is a further object of this invention to provide an improved apparatus for advancing thin metal leaf at variable speed with a heated die.
It is a further object of this invention to provide an improved apparatus and method for hot rotary stamping of metal leaf which may be combined with in-line gravure ink printing.